1. Field of the Invention
This invention relates to a multimedia packet communication system wherein, in multimedia packet communication of a plurality of qualities which is performed by way of a packet network, connections can be used automatically and dynamically to set quality classes individually in accordance with qualities required by applications while connection control is not performed directly by an application protocol.
2. Description of the Related Art
Attention is paid to an ATM (Asynchronous Transfer Mode) as a multimedia packet communication system which has a plurality of qualities. Conventionally, when it is tried to support a packet communication terminal in an ATM network, a connection oriented mode wherein a virtual circuit (VC) is set between calling and receiving terminals and a connectionless mode wherein such setting is not performed are available, and those modes are statically used separately for different applications. For example, in order to support short packet communication, file transfer communication and moving picture communication simultaneously, it is required for the individual application to first perform virtual circuit connection control directly and then perform packet transfer under a separate protocol. This is because a network protocol such as an IP (Internet Protocol) which makes an upper layer of an ATM network does not have a function of performing either of such connection and resource management.
A conventional protocol will be described in detail with reference to FIG. 4. In a data communication system based on a protocol such as a TCP (Transmission Control Protocol)/UDP (User Datagram Protocol)/IP (Internet Protocol), in order to support communication for a moving picture or an audio signal, an application 100 to be used with an ATM network 106 must be a stream type application wherein a packet is directly converted into cells without using the TCP/IP. Therefore, a protocol 104 for exclusive use for a moving picture and an audio signal must be prepared. Description will be given below how a connection is set in this instance.
Data of the TCP 102, a UDP 101 or the like use an ATM connection by way of the IP 103 which is a network layer. In one of connection setting methods, a connection is established by a signalling section 105 in accordance with a destination IP address of a packet to perform packet transfer. In this instance, however, a requirement for a quality from an upper layer is not discriminated by the IP 103 which is a network layer, and connection setting control is performed decisively by the signalling section 105. Since the IP 103 does not establish a connection and cannot distinguish a packet of the UDP 101 type and another packet of the TCP 102 of the connection type desired to be communicated from each other, it cannot selectively determine whether a packet should be sent in a connectionless mode or a connection should be established, and effective communication cannot be realized. Further, also in data transfer by the same TCP 102, since distinction between different quality packets cannot be performed by the IP 103 as in an FTP (File Transfer Protocol) or a remote terminal protocol called TELNET, if the address is the same, then a same connection may possibly be set, and consequently, quality control cannot be performed. Accordingly, when a file transfer application of an FTP or the like is desired to have an ATM connection having a special band, the application must necessarily start the signalling section 105 directly.
Meanwhile, in the case of the protocol 104 for exclusive use for a moving picture and an audio signal, the application must necessarily control the signalling section 105 directly without using an IP protocol to set a connection of a constant bit rate to effect communication.
As described above, in the conventional protocols, even when it is desired to switchably use connections of different qualities simultaneously and dynamically as In multimedia communication, connections must be started for each application, and the protocols are complicated with an application having a plurality of qualities. Consequently, there is a problem in that only static connection setting can be performed and effective packet communication cannot be performed.